Recovery of tungsten and vanadium from tungsten alloy scrap

This investigation resulted in the development of a flowsheet for the recovery of tungsten and vanadium from a leach solution of tungsten alloy scrap. The leach solution contained 95 kg/m3 WO3, 0.175 kg/m3 V and some other impurities. In the purification step, MgCl2 combined with Al2(SO4)3 was employed to remove the majority of Si, Al, P and Fe from the solution. This step was followed by converting tungsten and vanadium into the calcium salt with the addition of Ca(OH)2. When the mixed calcium salt was treated with formic acid solution, vanadium was selectively dissolved and separated from tungsten, while tungsten was rejected in the residue. The vanadium solution was then purified with H2SO4 and the ammonium meta-vanadate was precipitated with NH4OH to give 86.87% vanadium recovery. The leach residue of formic acid solution was dissolved with hot HCl solution in the presence of oxygen, resulting in the conversion of CaWO4 to H2WO4. This step was followed by NH4OH addition to convert H2WO4 to (NH4)2WO4 and removal of the remaining impurities. Finally, ammonium para-tungstate (APT) was crystallized from the solution of (NH4)2WO4 by evaporation. The purity of both tungsten and vanadium products met the standard specifications.